Mark and Kathy take their two-year-old son to the supermarket every Saturday. Each week, the same sequence of events unfolds: their son screams, demanding that they buy him treats. Although they refuse to give in to his demands,

, he continues to scream. His screaming is annoying and embarrassing for them. Finally, either Mark or Kathy get in their son's face and yell at the top of their lungs "Shut up." He stops screaming instantly. What operant conditioning concepts are illustrated in this story?
a) Although they are not aware of it, the parents are using negative reinforcement to increase their son's screaming.
b) The parents are in a very dysfunctional marriage; their child's screaming is his way of trying to get his parents to remain married.
c) The parents are using punishment to suppress the screaming; their use of punishment is negatively reinforced by the cessation of screaming.
d) Their son probably learned how to scream by observing his parents at home, and now he is reinforced on a variable-interval schedule of reinforcement.

C